Major emphasis is placed upon the study of Class I (restricted) and Class II (crossreacting) tumor antigens of the transplantation rejection type (TATA), and of tumor antigens (TA) assayed by in vivo and in vitro techniques and of the immune responses they evoke. As a corollary to this study, the biologic properties in vitro and in vivo of alien histocompatibility (H-2) antigens and of variant antigens in several neoplasms are under study. Solubilization and methods of purification of TATAs are under investigation with the ultimate purpose of defining these membrane and cytosol antigens, after purification, in physicochemical, biologic and molecular terms.